The present invention relates to multi-station machine tools in general, and more particularly to improvements in multi-station machine tools which comprise several pairs of spindles. Still more particularly, the invention relates to improvements in machine tools of the type wherein the spindles are disposed at the opposite sides of an indexible work supporting device.
It is already known to provide the frame of a machine tool with two spaced-apart carriers for rotary spindles which mount holders for suitable tools. The work supporting device is a turret which is indexible in the space between the carriers. The spindles cannot move axially in the respective carriers but the carriers are movable relative to the bed of the machine frame. A drawback of the just described machine tools is that they are suitable only for treatment of relatively short workpieces and that the tools can treat the workpieces only at their end faces or from within. Such machine tools cannot be used for the treatment of peripheral surfaces of relatively long workpieces in the form of shafts, rods or the like.
It is also known to treat relatively long workpieces in a machine tool wherein the workpieces are engaged by pairs of centers and the machine tool further comprises means which transmits torque to one end portion of a workpiece which is held between two centers. When a workpiece reaches a treating station, it is supported by a steady rest. The transfer of workpieces from station to station is effected by indexing a carrier for the centers. Reference may be had to German Pat. No. 1,271,501. The steady rests are indexed with the carrier. A drawback of such machine tools is that each workpiece must be centered prior to introduction into the first station in order to insure that the workpiece can be properly engaged by two aligned centers. Moreover, and since the workpieces are held between centers, their end faces cannot be subjected to any treatment. The peripheral surfaces of workpieces which are held by pairs of centers are treated by tools which are mounted on cross slides. This reduces the versatility of the machine tool and necessitates a separate treatment of end faces in a further machine.
It is further known to treat elongated rod-shaped or analogous workpieces in a series of machine tools which together form a production line. Each machine tool subjects the workpiece to a single treatment so that, if the number of necessary treatments is relatively high, the production line must consist of a large number of discrete machines which occupy much floor space and contribute significantly to the cost of finished workpieces. Moreover, a production line must be provided with several automatic (and hence complex and expensive) transfer apparatus which convey workpieces from machine tool to machine tool.